This invention relates to an exothermic heater device of the general type disclosed in U.S. Pat. Nos. 3,475,239 and 4,080,953, the disclosures of which are incorporated herein by reference. The heater device disclosed in U.S. Pat. No. 3,475,239 incorporates a flexible envelope which is divided into two separate sections and is attached by adhesive to an insulating backing pad. The envelope sections contain acid and base chemicals which are manually mixed together immediately prior to using the heater device. After the chemicals are mixed together and spread uniformally within the envelope sections, the envelope and pad are wrapped around a fiberglass pipe joint as shown in FIGS. 3 & 4 of the patent. Water is then injected into each envelope section and causes the chemicals to produce an exothermic reaction which generates heat for accelerating the curing of epoxy adhesive surrounding the pipe joint. The heater device may also be used for heating other articles and is not limited to heating only epoxy adhesive for accelerating the curing process.
It has been determined that the manual mixing of the chemicals and the spreading or distribution of the mixture to obtain uniform heating is time consuming, and if these steps are not performed properly, a safety problem can occur due to the mixed lime and acid powder which comprises the mixture. It has also been found that a precise amount of water is required in order for the heater to work properly and not generate an excessive amount of heat which may damage the fiberglass pipe. The heater devices disclosed in the '239 patent are also intended for use with a horizontal pipe coupling or a Tee connection into a horizontal pipe, as shown in FIG. 4 of the patent.